Is const_cast safe?

Question

I can\'t find much information on const_cast. The only info I could find (on Stack Overflow) is:

The const_cast<>() i

Answer 1

I can think of two situations where const_cast is safe and useful (there may be other valid cases).

One is when you have a const instance, reference, or pointer, and you want to pass a pointer or reference to an API that is not const-correct, but that you're CERTAIN won't modify the object. You can const_cast the pointer and pass it to the API, trusting that it won't really change anything. For example:

void log(char* text);   // Won't change text -- just const-incorrect

void my_func(const std::string& message)
{
    log(const_cast(&message.c_str()));
}

The other is if you're using an older compiler that doesn't implement 'mutable', and you want to create a class that is logically const but not bitwise const. You can const_cast 'this' within a const method and modify members of your class.

class MyClass
{
    char cached_data[10000]; // should be mutable
    bool cache_dirty;        // should also be mutable

  public:

    char getData(int index) const
    {
        if (cache_dirty)
        {
          MyClass* thisptr = const_cast(this);
          update_cache(thisptr->cached_data);
        }
        return cached_data[index];
    }
};